1. Field of the Invention
The present invention relates to a program length extending or shortening device and method, and a program length adjusting system, and more particularly to a program length adjusting system for adjusting the program length of a video program recorded on, for example, a magnetic tape, to an arbitrary length.
2. Description of the Related Art
In the conventional television station, a video tape recorder with a function of extending or shortening and adjusting the time length of a television program (hereinafter referred to as a program length) in accordance with the length of a commercial to be inserted was utilized.
Herein, the conventional video tape recorder of, for example, the analog recording method, records the image information in a unit of field on every recording track. Also, the digital video tape recorder of D-2 format records the image information in a unit of field on every plural recording tracks. Therefore, these video tape recorders allow the image information to be read and reproduced in a unit of field.
In such a video tape recorder for reading and reproducing the image information in a unit of field, a reproducing head unit is provided in which the tape run speed is controlled to be increased or decreased in accordance with a program length extending or shortening ratio, and the angle of incidence of the reproducing head is controlled to be deflected so that the head scan may follow the recording track, and a program play function is implemented by reading the image twice in a unit of field (two scans of recording track) or skipping the image in a unit of field (skip scan of recording track) in accordance with the increased or decreased tape run speed, using the reproducing head unit.
By the way, in recent years, a digital video tape recorder of the image information compression recording method has been used in which the recorded image information is compressed in the direction of time axis to enhance the recording efficiency.
In this digital video tape recorder of the image information compression recording method, the image information is compressed in a unit of frame (two fields), using a correlation between the fields, for example, and the compressed image information is recorded in a unit of frame on plural recording tracks. In the digital video tape recorder of such image information compression recording method, the compressed image can not be decoded unless the image is read by a unit of frame (two fields) or more from the recording tracks.
Therefore, with the digital video tape recorder of the image information compression recording method, there is a problem that if the program play function is performed by the reproducing head unit with the control of increasing or decreasing the tape run speed, the read compressed image is excessive or deficient by reading twice or skipping the recording track owing to the increased or decreased tape run speed, and may not be decoded.
For this reason, the digital video tape recorder of the image information compression recording method has no program play function and is desired to have the program play function.